DE19882417C2 - Non-porous, gas-permeable membrane - Google Patents

Abstract

A method of making compact, high gas flow, pollution-resistant gas filters based on making a continuous, extremely thin layer of a non-porous, gas-permeable polymer on the filter surface by coating one side of a microporous substrate with a dilute coating solution of a polymer contacted, preferably with the solution of an amorphous copolymer of perfluoro-2,2-dimethyl-1,3-dioxole, which polymer is simultaneously hydrophobic and oleophobic. The pore size of the substrate is specified in such a way that the polymer is filtered out of the solution as the solution flows through the substrate, as a result of which an extremely thin polymer layer remains. DOLLAR A solvent residues are deducted. The method for coating substrates in the form of foils and hollow fibers can be used, in particular for arrangements in modules consisting of a large number of hollow fibers. The coating prevents solid particles and liquid droplets from clogging the gas flow through the filter, and the filter can also be easily cleaned and reused. These coated fiber modules can be used as gas filters for gas flows with a high flow rate, including applications such. B. the collection of suspended droplets, the filtering of air in factories for microelectronic components or the filtering of ...

Description

FIELD OF THE INVENTION

This invention relates to a method of making gas permeable Membranes. More specifically, the invention relates to non-porous, gas permeable membranes for separating a gas from an aerosol, and in particular it relates to fluoropolymer Membrane filter to remove extremely fine, solid particles or liquid droplets, that are suspended in a gas.

BACKGROUND AND SUMMARY OF THE INVENTION

Numerous modern industrial processes involve a step of contacting Liquids or solids with a gas, being a suspension of liquid Droplets and / or solid particles is produced, which are distributed in the gas. Frequently is the suspended substance a dangerous or expensive material, or at least annoying contamination in a valuable gas stream. Therefore, one Filtration of droplets and particles from gases for numerous commercial applications increasingly important, such as to separate or limit the content of valuable or dangerous particulate materials, for ventilation of used ones and cleaned gases, which are to be disposed of in the environment, as well as for cleaning  of a contaminated gas stream that is used as raw material in a later process step should be used.

Membrane technology is increasingly used in the filtration of industrial gases applied. Because fluoropolymers have certain physical properties, such as for example good hydrophobicity, inertness to a variety of chemical and biological materials and also good thermal stability become such Materials commonly used in porous membrane filters, particularly microporous, expanded polytetrafluoroethylene ("E-PTFE"). A remarkable one The property is that oil wets the E-PTFE material. This wetting corresponds a measure of the affinity of a liquid for a particular membrane material. E- PTFE can be wetted by oil to such an extent that the pores are caused by the oil the membrane become blocked. This reduces the gas flow through the membrane and sometimes completely prevented. Oil is used in a variety of applications, in Within the framework of which process stages are carried out on the basis of gases, such as Example for hydraulic compression or for applications based on Engines. As a result, the oleophilic nature of the E-PTFE material limits it Effectiveness in the context of membrane filtration considerably.

In order to improve the effectiveness of such gas filtration, according to one gas permeable membrane has been sought, which both pronounced hydrophobicity, as well Has oleophobia. U.S. Patent No. 5,554,414 to Moya et al Process for producing a porous composite material Product, said article being a porous, polymeric substrate and has a hydrophobic / oleophobic, polymeric surface, which is based on a crosslinked, ethylenically unsaturated monomer has been produced, the one Contains fluoroalkyl group. The polymeric surface is made by using a substrate in the form of a porous membrane with a solution of a polymerizable monomer, a Crosslinker and a polymerization initiator coated. The polymerizable monomer is polymerized onto the surface of the substrate in the form of the porous membrane and networked, and in such a way that thereby the entire surface of the porous membrane, including the inner surfaces of the porous membrane a cross-linked polymer is modified. However, this remains from a composite material  existing, porous product essentially all of the original properties of the Substrate, especially the porosity.

Bowser U.S. Patent No. 5,166,650 describes the use of an amorphous A copolymer for a gas filter, said amorphous copolymer being 10 to 40 mol% Tetrafluoroethylene ("TFE") and a complementary amount of perfluoro-2,2-dimethyl-1,3-dioxole ("PDD") contains. This amorphous copolymer becomes a gas-permeable material coated, which passes through the material, or continuous Has pores. The amorphous copolymer coats at least part of the interior of these passages, however, does not lead to their blocking.

The references cited above describe completely porous membranes that are used for Gas filtration are suitable. With the help of the passages formed by the pores, the Gas molecules easily migrate through the entire structure. Therefore allow such porous structures generally have a high gas flow, which as the Gas permeability is defined per unit area of the filter surface. Thus, usually a porous filter element of moderate size with a gas for converting industrial purposes to acceptable speeds. Although the pores however, are coated with compositions of increased oleophobicity to the The open pores offer the oil a reduction in the tendency of the oil to adhere to the membrane still sufficient opportunity to penetrate the membrane and eventually close it clog. Solid particles suspended in a gas can also enter the membrane penetrate and clog the pores. It can also penetrate, liquid and solid Toxins are embedded in the pores and then difficult to clean again by cleaning be removed. This can be done through a gas filter in the form of a porous membrane possible gas flow decrease over the life of such a filter.

Reference US-A-5 258 202 discloses methods of manufacture and use improved, microporous hollow fibers as well as existing from such fibers Tube bundle. Literature US-A-5 238 471 discloses using spray methods applied fluoropolymers, which can be used as membranes suitable for gas separation are. Document US-PS-4,767,643 discloses a method for continuous Vacuum impregnation of a fibrous film material. U.S. Patent 4,243,701 discloses the production of membranes suitable for gas separation. The  Literature US Pat. No. 4,214,020 discloses methods of coating hollow bundles of fiber membranes. Literature EP-A1-0 649 676 discloses the Aftertreatment of membranes suitable for gas separation with a fluorine-containing one Polymer. Literature EP-A1-0 641 594 discloses an oil and water repellent, gas permeable filter. Literature WO-A1-90 / 15 662 discloses perfluorodioxole membranes.

Until recently, a non-porous, permeable membrane is suitable for practical purposes not available for a gas filter. The gas flow through a non-porous, permeable membrane is directly proportional to the permeability of the Membrane composition, and also inversely proportional to the membrane thickness. The most polymeric compositions have low gas permeability. Around thus a filter element with a size useful for practical purposes and an inner To provide a surface that is simultaneously used for industrial applications usable gas flow, a non-porous membrane with a Permeability of only moderate height should be extremely thin. Until now according to the prior art, no method is known for producing a sufficiently thin, Manufacture non-porous, gas-permeable membrane that is suitable for a gas filter.

A method for producing a membrane has now been found, the one extraordinarily thin, continuous layer of a non-porous, gas-permeable Includes polymer composition. The polymer composition has one excellent permeability on what a high, original gas flow with it brings. In addition, the non-porous structure is based on the continuous layer improved resistance to oil and solid particle penetration and one increased stability of the gas flow. In the event that the new membrane dirty, you can also clean them without difficulty, so that the gas flow is set again according to a gas permeability rate that is almost the same Corresponds to the initial value. As a consequence of this invention, it is now possible to use the The basis of a non-porous, gas-permeable polymer is a very thin film in one Manufacture membrane, which one for use as a gas filter and for others Can use operations that are associated with the passage of gases.  

Accordingly, this invention provides a method of making a membrane comprising the following steps:

• a) dissolving a gas-permeable polymer in a solvent so that a Coating solution is obtained;
• b) Selecting a microporous substrate with a pore size, on the basis of which one can effectively filter out the dissolved polymer from the coating solution, which substrate has first and second sides;
• c) contacting the first side of the microporous substrate with the Coating solution;
• d) causing the solvent to pass through the microporous substrate onto the second side flows;
• e) removing the coating solution and the solvent from the membrane; and
• f) withdrawing the solvent from the membrane, whereby a continuous, non-porous layer of the gas-permeable polymer is formed.

In a further aspect, the present invention also provides a method for Coating hollow fibers with an ultra-thin, continuous layer of one gas permeable polymer.

A method for producing a gas filter is also provided, which comprises the following steps:

• a) dissolving a gas-permeable polymer in a solvent so that a Coating solution is obtained;
• b) Providing a filter module, which comprises the following components:
  • 1. an elongated housing with two ends, the housing defining a sleeve-side cavity;
  • 2. a first tube disk arranged at one end of the housing and having a first outer surface arranged outside the housing;
  • 3. a second tube disc arranged at the other end of the housing with a second outer surface arranged outside the housing;
  • 4. A plurality of open-ended, microporous, hollow fibers that extend within the housing within a substantially parallel arrangement from the first outer surface located outside the housing to the second outer surface located outside the housing, these hollow fibers together define a tube-side cavity; wherein, based on the pore size of the hollow fibers, the dissolved polymer can be effectively filtered out of the coating solution; and
  • 5. at least one connection leading through the housing in the region of the sleeve-side cavity;
• c) Cause that the coating solution through one of the sleeve side Cavities and the tube-side cavities flows;
• d) Have the solvent from the coating solution pass through the microporous hollow fibers through to the other side of the sleeve Cavity and the tube-side cavity flows;
• e) removing the coating solution and the solvent from the module; and
• f) withdrawing the solvent from the hollow fibers, which on one side of the Hollow fibers a continuous, non-porous layer of the gas-permeable polymer is formed.

In another aspect, the present invention provides a method for Separation of a gas from an aerosol is available, which does the following includes:

Flow of a gas through the area of a membrane corresponding to a filter surface, which comprises the following components:
a microporous substrate; and
a non-porous, gas-permeable layer which is applied continuously to the substrate and to the entire area corresponding to the filter surface, which layer consists of an amorphous copolymer based on the compound perfluoro-2,2-dimethyl-1,3-dioxole and which layer also has an oxygen permeability of at least 100 barrers at a temperature below the glass transition point of the amorphous copolymer.

In addition, a novel gas filter is also provided which comprises a membrane with a region of the filter surface which is suitable for the passage of a gas so that suspended droplets can be separated from this gas, the membrane comprising the following components:
a microporous substrate with a pore size of about 0.005 to 0.1 µm; and
a non-porous, gas-permeable layer which is applied continuously to the substrate and to the entire area corresponding to the filter surface, which layer consists of an amorphous copolymer based on the compound perfluoro-2,2-dimethyl-1,3-dioxole and which layer also has an oxygen permeability of at least 100 barrers at a temperature below the glass transition point of the amorphous copolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a compact gas filter module based on hollow fibers in accordance with the present invention.

FIG. 2 illustrates the view of a detail of a portion of the gas filter module of FIG. 1.

Figure 3 is a schematic diagram of an apparatus that can be used to apply a thin layer of a gas permeable polymer to the hollow fibers of a gas filter module in accordance with the method of the present invention.

Figure 4 is a schematic diagram of another apparatus that can be used to apply a thin layer of a gas permeable polymer to the hollow fibers of a gas filter module in accordance with the method of the present invention.

FIG. 5 shows a schematic diagram of an apparatus with which the resistance of gas filters containing membranes to wetting can be checked.

FIG. 6 shows a cross-sectional view of the holding device for flat membrane films shown in FIG. 5.

DETAILED DESCRIPTION

In one aspect, the present invention includes a method for Separation of a gas from an aerosol. The term "aerosol" means one Suspension of fine, liquid droplets or solid particles (in the text below is both called the common term "droplet" in a gas. The The invention is suitable for simultaneously dispensing liquid droplets, solid particles or both filter. Thus, the present invention can also be used to: to produce more concentrated aerosol by adding a certain proportion of the gas removed, or by further removing substantially all of the gas so as to to collect the droplets. The cleaned, outflowing gas is essentially free of Be droplets, so that the invention can also be used from an aerosol to get purified gas.

The size of the droplets can depend on various factors. These can Include system pressure and temperature, as well as physical properties of the Droplets, such as composition and viscosity of the liquid, and also the method by which said droplets were made, such as such as condensation and atomization.

The drops can be of uniform size or a certain size distribution exhibit. Generally the size of the droplets suspended in the aerosol corresponds a numerical value in the range from approximately 0.01 μm to approximately 1 mm. The concentration of Droplets are irrelevant according to the invention. However, it should be noted that usually coalesce liquid droplets in the event of contact.

The separation is carried out by passing the gas through a gas filter filtered, which has a gas permeable membrane. As part of the aerosol used the properties of the gas are not of particular importance as long as the gas is used  Is able to penetrate the membrane. However, you have to assume, of course can that the gas the materials from which the membrane is built, or also the Parts of the gas filter to which the gas is exposed are in no way adversely affected or even affected reacted with the materials mentioned. Typical, gaseous according to the invention Components include elementary gases such as helium, hydrogen, neon, Nitrogen, argon, oxygen, krypton and xenon, hydrocarbons, such as Methane, ethylene, ethane, acetylene, propane, propylene, cyclopropane, butane and butylene; also halogenated carbon compounds or halogenated hydrocarbons, such as Example dichlorodifluoromethane, methylene chloride and methyl chloride; Also various gases used in industry or in the environment, such as for example nitrogen oxides, carbon dioxide, ozone, hydrogen sulfide, ammonia, Sulfur dioxide, carbon monoxide, phosgene and any conceivable mixture of the above enumerated gases.

One element of the membrane corresponds to a non-porous film made of a gas-permeable Substance. The gas-permeable substance preferably corresponds to an amorphous one Copolymer based on a certain perfluorinated dioxole monomer, namely in particular based on the compound perfluoro-2,2-dimethyl-1,3-dioxole ("PDD"). in the Within the framework of some preferred embodiments, the copolymer is based on PDD copolymerized, and also based on at least one other monomer which selected from the group consisting of the following compounds: Tetrafluoroethylene ("TFE"), perfluoromethyl vinyl ether, vinylidene fluoride and Chlorotrifluoroethylene. In the context of other preferred embodiments the copolymer is a dipolymer based on PDD and a complementary one Amount of TFE, which is in particular a polymer containing PDD can act according to a numerical value in the range of 50 to 95 mol%. examples for such dipolymers are described in more detail in U.S. Patent No. 4,754,009 issued to E. N. Squire on June 28, 1988, and described in U.S. Patent No. 4,530,569, also edited by E. N. Squire on July 23, 1985. Perfluorinated dioxole monomers are disclosed in U.S. Patent No. 4,565,855 issued to B.C. Anderson, D.C. England and P.R. Resnick was released on January 21, 1986. The revelation content of this mentioned US patents are hereby incorporated by reference into the present Description to be included.  

The amorphous copolymer can be characterized using its glass transition temperature ("T _g "). According to the prior art, the glass transition temperature as a polymer property is well known to the person skilled in the art. It corresponds to the temperature at which the brittle, translucent or glassy initial state of the copolymer changes into a rubbery or plastic state. The glass transition temperature of the amorphous copolymer depends on the composition of a given copolymer used in the membrane, in particular on the amount of TFE or other comonomer that may be present. Examples of T _{g are} shown in FIG. 1 of the above-mentioned US Pat. No. 4,754,009 by EN Squire, these numerical values being approximately 260 ° C. for the case of dipolymers containing 15% tetrafluoroethylene comonomer extend to less than 100 ° C in the case of dipolymers containing at least 60 mol% tetrafluoroethylene. However, it can be assumed that the copolymers based on the compound perfluoro-2,2-dimethyl-1,3-dioxole according to this invention can be "tailored", so to speak, so that a T _g value can be achieved which is sufficient is high in order to be able to expose the membrane produced on the basis of such a composition to the temperatures of water vapor without damage. Therefore, the membranes of this invention can be designed so that they can be steam sterilized so that they can be used for a variety of applications in which sterile materials are required, particularly those for which one deals with biological materials. Preferably, the glass transition temperature of the amorphous copolymer should be at least 115 ° C.

In addition, the amorphous copolymer exhibits considerable hydrophobicity and oleophobicity characterized. This incompatibility of the PDD copolymer with both water, as well with oil causes the gas permeable membrane to be within a wide range of Solvents are only soluble or to a negligible extent is capable of swelling. This characteristic ensures that in the course of the contact with a variety of liquid compositions the structure of the membrane undamaged is maintained and that at the same time their dimensions are not changed.

The outer shape of the membrane according to the present invention can be flat Foil or any other geometric configuration. A flat film may include one or more monolithic film (s) made from the  non-porous, gas-permeable substance exists. The through a permeable Gas flow through the membrane is inversely proportional to the thickness and direct proportional to the area of the membrane available for gas transport. A relevant pre-trained specialist will immediately understand that one very thin film should be used to pass through a gas permeable film with a practical surface size, a gas flow that is acceptable in practice to be able to receive. This finding is still taking into account the fact correct that the permeability of numerous commercially important gases through that Amorphous copolymer is relatively high, which is within the scope of the present Invention is preferably used. To the gas flow required according to the invention realize, the preferred thickness of a non-porous film corresponds to a numerical value in Range from about 0.01 to about 25 µm.

In general, a polymer film with a thickness of less than 12 μm cannot be used perform self-supporting. Accordingly, the gas permeable membrane comprises an amorphous according to this invention in a preferred embodiment Copolymer that is in the form of a non-porous layer on a microporous substrate is present. This substrate ensures that the initial structure of the non-porous layer in the Is not affected by their use. The structure of the substrate should be like this be designed so that sufficient porosity is provided to the flow of not hinder gaseous component. Typical examples of such porous Substrates include a perforated film; also a porous, sieve-like fabric; a monolithic, microporous polymer film; a microporous hollow fiber as well any combination based on the materials enumerated above.

The non-porous layer is next to or directly on the microporous substrate arranged and can with the help of a variety of methods known to those skilled in the art be produced, including coating techniques such as Diving, spraying, painting or spreading. Preferably you can apply a non-porous layer using a solvent coating method, and particularly preferably with the help of a new type of solvent Coating method that explains in more detail in the text below will be and which method is suitable for a microporous substrate to place an extremely thin, continuous, non-porous layer of an amorphous copolymer.  

With regard to the thickness of the non-porous layer, the expression "extremely thin" corresponds to a numerical value in the range from approximately 0.01 to approximately 10 μm.

The membrane can also have a tubular structure. A hollow fiber provides for use in the context of the present invention a particularly preferred form of a substrate. The term "hollow fiber" refers to articles having a high aspect ratio and extremely small dimensions in the direction of the cross section of these items. With the expression "high aspect ratio" is the ratio of Fiber length means the dimensions of the fiber cross section. Though others, hollow ones external forms are possible and expressly as part of the teaching of the present According to the invention, cylindrical hollow fibers are preferred. In general the outer and inner fiber diameter corresponds to a numerical value in the range from about 0.1 to 1 mm, or from about 0.05 to 0.8 mm. Basically it will Separation process according to this invention carried out so that the gas permeable membrane component of a membrane in a gas filter with the aerosol in Brings contact and thus allows the gas to penetrate through the membrane, leaving the droplets present in the aerosol. The expression "Filter surface size" corresponds to that actually available for gas transport standing area. In general, this filter surface area is actually the same as for the gas transport available area of the membrane, measured in the direction of the Gas flow perpendicular direction. For example, the Filter surface size of a membrane in the form of a rectangular, flat film the product from the length and width of the film. Similarly, the filter surface size corresponds a single, cylindrical hollow fiber the product of the fiber length and the Circumference of the cylinder.

The preference for a substrate in the form of a hollow fiber is based on the ability of one such a substrate, based on a small volume, a considerable one Realize filter surface area, in particular within a volume an overall small cross-sectional area. The filter surface size of a hollow fiber per Volume of fiber increases inversely proportional to the fiber diameter. Consequently the density corresponds to the surface size of a single hollow fiber with a low one Diameter of a very large value. You can also get a substantial Number of fibers in a substantially parallel to the axis according to the fiber course  bundle arranged direction and thus a consisting of a plurality of fibers Build system. In fact, through such a procedure, one can realize the total realized Filter surface size to the sum of the individual filter surface sizes of the bundled Approximate fibers. Due to the fiber geometry, the total can actually be achieved Filter surface size of a bundle consisting of hollow fibers a multiple of total cross-sectional area of the gas filter unit. Are hollow fibers preferred as a substrate because the surface size in this case is very high enables effective contacting of the aerosol. This is due to the fact that the Conduct aerosol flow in the direction of the fiber axis through the bundled hollow fibers can, in such a way that the aerosol over the entire available gas filter area is distributed. In contrast to that, with a gas filter the basis of filter elements in the form of flat foils occur "dead spaces" that are hardly of Flushed aerosol, and / or already filtered gas, whose contact with the Filter elements stagnated, which naturally means that the transfer rate through such filter elements is lowered. Nevertheless, one can on the basis of a corresponding Teaching of the present invention, extremely thin, non-porous layer that is applied to a substrate in the form of a flat film, but still highly realize effective and very practical gas filter.

According to the present invention, the non-porous layer extends on the base of amorphous copolymer continuously over the entire range of Membrane surface, which is available as a gas filter. That means the non-porous Layer without any gap covering the entire substrate and essentially no defects, Breakthroughs or other openings that could lead to a not open penetration through the membrane based, open passage is realized by which one for gaseous substances between the aerosol side and the gas side of the gas filter Connection is created. The non-porous layer is preferably located on the Aerosol side of the gas permeable membrane. One can say that the non-porous Layer the penetration of liquid droplets or solid particles into the micropores of the Membrane provides an insurmountable barrier. Thus, in the course of Separation process according to the present invention enables a high gas flow, the gas filter is also less susceptible to possible clogging, so that the said high gas flow remains stable even in the course of a longer operating period. In addition, the liquid droplets and the solid particles due to the barrier in  Form of the non-porous layer can also not be embedded in the membrane. If As a result, the filter should be contaminated, so it can be used without difficulty clean while restoring filter performance based on a gas flow which almost corresponds to the original characteristic.

In contrast to the present invention, they are based on the prior art usual aerosol gas filters, such as that mentioned above, that of Mayo and co-workers has been disclosed on one with hydrophobic and oleophobic material coated, microporous structure. We know that in such filters the mechanism The gas filtration is based on the fact that the gas flow through narrow and complicated, but open, pore-like passages take place, which extend over the entire thickness of the used Structure. In this case, the coated material prevents penetration Substances in the said passages in no way. So in the case of one Use of the gas filter according to the present invention has both durability of the filter against possible clogging, as well as the stability of the gas flow appropriate characteristic of filters customary in the prior art.

The lack of said passages means that the gas filter corresponds to the The present invention is particularly suitable for the processing of such gases which biological fluids are contacted. The expression "biological fluids" includes both human and animal, natural body fluids, such as Example blood, and also natural or synthetic or from a corresponding Combination of existing media for cell cultures. Such fluids usually contain Cells and other microorganisms, which tend to be numerous Adhering and growing substrate materials. While porous membranes based of PDD copolymer may well be resistant to such adhesion and for one a certain amount of time even when using systems based on biological fluids can maintain good gas flow, it is still possible that in the pores cells and microorganisms can grow until the gas flow is finally stopped becomes. Such microorganisms can, however, the non-porous layer of the novel Do not penetrate the gas filter. If, in addition, on the gas filter surface of the non-porous layer, cell growth or other contaminants actually occur should, so said surface can be cleaned without difficulty to this Way to restore the filter performance described above.  

PDD-containing amorphous copolymer is permeated by gases with a high degree of selectivity, particularly with regard to oxygen and nitrogen. This O ₂ / N ₂ selectivity represents a function of the PDD content in said PDD copolymer. The oxygen-nitrogen selectivity of a PDD copolymer containing 50 to 90 mol% of PDD corresponds to a number ratio of at least approximately 1.5: 1. This distinctive gas selectivity of the PDD copolymer can usually be used to test whether the gas-permeable element of the membrane is non-porous. For example, one can easily check whether there are holes in the membrane by gradually exposing one side of the membrane to certain predetermined, pure gas components under constant pressure. By then calculating the ratio of the individual gas flows that occur, the selectivity can then be determined.

If the gas flow is roughly comparable for each individual gas, this is an indication to consider the possibility that the non-porous layer could be faulty (by for example, it has openings or even holes). However, confirmed the other way around also the presence of the desired, high gas selectivity that the gas permeable layer is not porous. Because the non-porous, amorphous copolymer layer of this invention is extremely thin changes in the selected process technology are already at risk accompanied by producing a defective, gas-permeable layer in this way. Therefore it may be helpful to ensure that the non-porous layer is in perfect condition.

The novel gas separation process is usually carried out at about room temperature, although it is also possible to carry out the process at higher temperatures. However, the gas-permeable membranes containing PDD copolymer should be used at a temperature which is lower than the glass transition temperature of the material, in particular at a temperature which is at least 30 ° C. lower than the glass transition temperature of the amorphous copolymer which is within the scope of the non-porous layer is used. As explained in the text above, PDD copolymers can have a remarkably high T _g . Therefore, the amorphous copolymer membranes used in the method of the present invention are suitable for use at elevated temperatures, including some embodiments that can be used at temperatures above 100 ° C. The method according to the present invention can also be carried out at relatively low temperatures, for example at about 10 ° C. However, the gas filter should of course not be used at temperatures outside the temperature range within which the substrate material used is still usable.

In accordance with the teachings of this invention, a new process has been discovered which placing an extremely thin polymer layer on a microporous substrate enables. The novel method can be based on any suitable method Perform high molecular weight polymers that dissolve in one liquid solvent of low viscosity is suitable. However, this should Of course, solvents do not dissolve the substrate material used with the material react or otherwise degrade it. As mentioned above, amorphous Copolymers based on PDD and TFE preferred to be resistant to wetting Manufacture membranes for gas filters. As part of the implementation of the novel Certain "perfluoro" solvents can be used to process these PDD / TFE Dissolve copolymers. Suitable perfluoro solvents include certain, largely or completely fluorine-substituted hydrocarbon compounds or Fluorocarbons containing ether-oxygen bridges. Typical examples for perfluorinated solvents used in the novel process are suitable include perfluoroalkanes such as perfluorohexane, Perfluorheptan and Perfluorooctane, under the brand names PF5060, PF5070 and PF5080 by 3M Company, Minneapolis, Minnesota / U.S.A. are available, as well as the material also available from 3M, called FC-75 Fluorinert brand electronic liquid. The material labeled FC-75 is a solvent based on perfluoro compounds which mainly have 8 carbon atoms, where the material is believed to contain the compound 2-butyltetrahydrofuran.

The novel process involves a high resolution of the polymer Molecular weight in a solvent, creating a dilute coating solution will be produced. Then a suitable, microporous substrate is selected with the help which can effectively filter the polymer out of the coating solution. The coating solution is then coated with a first side of the microporous substrate  contacted. Then the solvent is caused to pass through the microporous substrate flow through to the second side of the substrate, which is the first side is arranged opposite. This flow continues while on the first Side builds a layer made of the high molecular weight polymer. As soon as this polymer layer has built up to a predetermined thickness, removed the solution contacting the first side is made from the same. After that, the remaining inside the pores and in the moist polymer layer Solvent residues deducted.

The concentration of the solution depends on various process parameters, such as for example the composition of the dissolved polymer and the pore size of the microporous substrate. Preferably, the concentration of the polymer in the diluted solution correspond to a numerical value of less than approximately 1% by weight, particularly preferably a numerical value of less than about 0.5% by weight and in particular a numerical value of less than about 0.1% by weight.

The term "filter out effectively" in this context means that the substrate is a barrier to the dissolved polymer molecules, to which However, the solvent used allows the flow. Thus the pore size of the used substrate in relation to the size of the polymer molecules dissolved. The means that the pore size of the substrate must be small enough to separate the polymer from the filter used solvent.

A preferred technique to select a substrate with an appropriate pore size that one can use in the context of the novel process, takes both into account Molecular weight of the gas permeable polymer, as well as the desired gas flow should have the membrane obtained as a product. After getting a gas permeable Polymer is selected, the molecular size of the polymer in the solution can then without determine more. For example, PDD copolymer usually has one Molecular weight of about 600,000. A microporous filter with a Selection limit for molecular weights ("MWCO"; from English: "molecular weight cut off") above 50,000, a solution of such a PDD copolymer in an effective manner can filter. According to one from Osmonics, Inc., Minnetonka, Minnesota / U.S.A. published filter spectrum corresponds to the nominal size of a  Polymer molecule with a molecular weight of 50,000 on the numerical scale of the Saccharide type a numerical value in the range of about 0.02 to 0.03 microns.

To convince yourself that the substrate used is actually the dissolved one Filtering out polymer in an effective manner, one can check if that after the passage Solvents drawn off the substrate are essentially free of dissolved polymer is. However, it is not necessary that the filtrate obtained be of dissolved polymer is completely free. Certain gas-permeable polymers that are used in the teaching of present invention may have a wide range Molecular weight distribution on what is indicated by a corresponding weight average of Molecular weight is marked. Accordingly, such a distribution certain high and low molecular weight fractions whose Molecular weight value is higher or lower than the average molecular weight. In such a case, the substrate will contain most of the high polymer fractions Filter out molecular weight, while using for a certain fraction of the fractions low molecular weight allows passage. Preferably that is the filtrate obtained is regarded as essentially free of polymer dissolved therein, if the Concentration of the dissolved polymer in said filtrate has a numerical value of less than about 10% of the concentration that the dissolved polymer in the Has coating solution. One can check whether the filtrate is essentially is free of polymer dissolved therein, use various suitable ways. So you can, for example, perform a chemical analysis on a sample of the filtrate, wherein the polymer content can be determined quantitatively, or alternatively draw off the solvent from a sample of the filtrate in order to remove the To show the presence of a polymer residue. A preferred method to check if Effective filtration has actually occurred, including measuring the viscosity of the liquid filtrate, which is then measured with the viscosity of the pure Solvent is compared.

In this case, the filtrate is considered to be sufficiently free of polymer dissolved therein, if the The viscosity of the filtrate roughly corresponds to the viscosity of the pure solvent.

The predetermined pore size of the substrate should not be too small, since an extremely small pore size of the microporous substrate can result in a restriction of the gas flow. The lower limit of the pore size of the substrate should preferably be selected so that a gas flow is made possible which is at least about five times as large as the gas flow of the desired, non-porous polymer layer. For example, the oxygen flow of a 0.5 μm thick layer of an amorphous PDD / TFE copolymer with a T _g value of 240 ° C. is approximately 2,000 gas permeability units (“GPU”; from English: “gas permeation units”). Such a gas permeability unit is defined as follows: 1 cm ³ / cm ² -sec-cm Hg × 10 ^-6 . In this case, the gas flow through the pure substrate should be at least 10,000 GPU. Hollow fibers made of polysulfone with a pore size corresponding to a MWCO value of 50,000 can be assigned a gas flow corresponding to a numerical value of 240,000 GPU. Accordingly, in this example the minimum thickness of a layer consisting of PDD / TFE copolymer with a T _g value of 240 ° C. on polysulfone should correspond to a numerical value of approximately 0.02 μm, which would correspond to a gas flow of approximately 48,000 GPU.

You can also see the meaning of the expression "polymer with a molecular weight appropriately sized "in that the molecular weight of the polymer is predefined in such a way that a molecule is made available, the size of which sufficient to pass through the microporous substrate used from the polymer solution to be filtered out. The pore size of the microporous substrate should be small enough be specified in order to filter out the polymer used from the solution. The microporous substrate should have a pore size corresponding to a selection limit (= MWCO- Value) which is lower than the molecular weight of the polymer used. Preferably, the selection characteristic (= MWCO value) of the substrate should be at most a numerical value of about 50% of the molecular weight of the polymer used correspond, and particularly preferably at most a numerical value of about 20% of Molecular weight of the polymer used.

Solvent residues can be removed by, for example, purging the membrane under pressure using a clean, inert gas stream, by applying a vacuum to the membrane, or alternatively using a combination of these two measures. The stripping continues until all of the solvent residues have actually dried the membrane. This actual dryness is reached when the gas flow through the membrane, such as the flow of gases O ₂ and N ₂ , remains unchanged under certain boundary conditions (such as pressure and temperature) that prevail during the penetration process. The excess solvent can be drawn off in any direction across the thickness of the membrane. However, when using the method of flushing the membrane, the gas used for flushing is preferably applied to the coated side of the structure. If a vacuum is used, it is preferably applied to the second side of the membrane in order to suck the solvent residues present from the first side to the second side of the membrane. Although the pressure of the inert gas used or the negative pressure of the vacuum applied is not essential to the invention, exposure of the membrane to an excessively large pressure difference should nevertheless be avoided in order to avoid a hole being torn into the membrane due to excessive blowing or suction. In general, a low pressure or a slight vacuum is sufficient to complete the solvent residue removal step in a few hours. This stripping is preferably carried out at room temperature. However, the solvent can also be removed at elevated temperature, but with the proviso that the substrate, the polymer and the apparatus used to hold the membrane must not be adversely affected.

In particular for coating hollow fibers, the flow rate for pulling off is Solvent residues on the non-porous layer of inflated gas are very important. The Gas purging should flow at a high rate over the entire surface of the non-porous Layer take place in order to effectively prevent the polymer from being on the substrate drying to a non-uniform thickness, such as in the form of lumps. in the Such clumps can be coated on the inner surface of hollow fibers clog the clear openings of the fibers. If the gas flow rate is sufficiently high is used as the basis, the non-porous layer will correspond to its given Dry the layer thickness over the entire substrate to a uniform layer thickness. The Relevant pre-trained average specialist should be without unreasonable, additional experimental effort to be able to do so in the course of such a gas purge to determine the minimum flow rate required to produce a coating with uniform thickness is required.

One can carry out the novel procedure in the course of a single cycle, or alternatively in the course of a series of cycles. As part of carrying out the procedure  as a single cycle, the step of sucking solvent through the microporous Carried out substrate until the polymer layer has the predetermined layer thickness. Alternatively, a sequence of process steps can be repeated many times in succession be, which each consists of a step in which solvent through the Sucks through substrate, and from a further step in which the solvent is removed becomes. The overall thickness increases as part of each sequence carried out in this way the polymer layer to some extent. The repeated implementation of such Process cycles can be continued until the has built up the desired layer thickness.

The novel method can be used to coat a Substrate in the form of a hollow fiber can be used. As mentioned above, at Hollow fibers, the density of the available filter surface is extremely high his. Using the present method, the entire range of Cover the filter surface of a fiber with a continuous, extremely thin layer that consists of a non-porous, gas-permeable polymer. With the help of the novel The process can thus be a tubular membrane with an extraordinarily high Preserve the density of the filter surface because the gas-permeable polymer layer is pronounced is thin.

Gas filters are often designed so that they have a high capacity with a small volume exhibit. This is because you are trying to achieve maximum gas flow with one at the same time to connect minimal pressure drop within the entire filter, whereby overall small dimensions of the filter cross section can also be provided. The Coating methods according to this invention also provide the possibility sure to manufacture a module suitable for use in a gas filter that contains a large number of densely packed, coated hollow fibers. Hence the teaching of present invention additionally associated with the advantageous technical effect, a Possibility to manufacture a compact gas filter with a very high capacity to provide.

Although a large number of external shapes is conceivable for such a module, a generally cylindrical structure is preferred according to the invention. A cylindrical gas filter can be manufactured without difficulty and can also be easily inserted into existing processes, often by simply connecting such modules in the context of a pipeline with the help of suitable pipe flanges. In addition, the circular cross section of a cylindrical gas filter also enables a large number of individual fibers to be packed together per unit area of the total available cross sectional area of such a filter. It is thus possible to produce a relatively compact gas filter, which at the same time has an extremely large filter surface, by packing a very large number of fibers together. For example, in the course of coating a hollow fiber made of polypropylene with an outer diameter of 250 μm per unit volume, a gas transport area of 16.4 cm ² / cm ^{3 is obtained} , the density of the fiber packing being 40%. The packing density corresponds to the percentage of the cross-sectional area of all fibers in the cross-sectional area of the entire gas filter. In the case of a cylindrical gas filter, the cross section is measured perpendicular to the cylinder axis. In contrast, the typical surface density for the case of a membrane with a geometry corresponding to a flat film is only 1.1 cm ² / cm ³ , which corresponds to only one sixteenth of the value of packed hollow fibers.

In addition, the polymer used in the context of the present invention also has one extraordinarily high gas permeability. For example, membranes on the Based on PDD / TFE copolymer an oxygen permeability corresponding to one Numerical value of at least 100 barrers, preferably at least 200 barrers and especially at least 500 barrers.

Consequently, a gas filter can be provided based on the present method be, the gas flow is the corresponding, with the help of the state of the art Filters obtained using conventional methods is superior to what is described above Combination of a high gas permeability and an extremely thin, from the non-porous Membrane composition is due to existing layer, as well as on the offered in a compact space, high value of the filter surface size.

In the context of Fig. 1, a gas filter module is shown on the basis of hollow fibers suitable for use in the present invention. The filter module 10 has a generally elongated, cylindrical housing 2 , in which a multiplicity of hollow fibers 4 are located. These fibers are held in a fixed position by means of tube disks 8 . The fibers run through the tube disks so that the free ends 5 are able to protrude up to the outer surfaces 9 of these tube disks. The actual filter surface area of each individual fiber is defined by the fiber diameter and the distance between the tube disks.

From Fig. 1 it is apparent that the fibers are aligned exactly parallel. However, this corresponds to an ideal state, which is not absolutely necessary in practice and will generally not exist. Due to the extremely high aspect ratio of length to diameter and the polymeric composition of the fiber material, each individual fiber is relatively flexible. It is readily acceptable for practical purposes that the fibers are only substantially parallel, provided that the space between adjacent fibers is sufficient to effectively contact most of the outer surface of all fibers with the gas to enable. The interior of the housing, the exterior of the fibers and the surfaces arranged on the inside on the inside of the tube disks together define the sleeve-side cavity 6 . The housing is provided with at least one connection 7 a, 7 b in order to allow a gas flow into the interior of the sleeve-side cavity or out of this cavity.

The module can also expediently be installed in a gas filter provided with the covers ( 31 , 32 in FIG. 3), which covers can be fastened over the outer surfaces of the tube disks. These covers define inlet and outlet chambers, respectively, which serve to conduct fluids into and out of the lines. The free space inside the hollow fibers and within said inlet and outlet chambers, insofar as these are present, is referred to below as the tube-side cavity. In the embodiment shown in FIG. 2, the inner gas filter surface 22 of each individual fiber 24 is covered with a layer consisting of gas-permeable polymer 26 . In the context of an embodiment which has also been considered but not shown here, the gas-permeable layer mentioned can also be used to coat the outer surface 28 of the fiber. Of Fig. 2 it can be seen that the fiber is stable embedded in the tube plate so that a fluid tight seal is effected between the sleeve-side cavity and the tube side cavity.

Such modules based on hollow fibers can be produced using fibers made of different materials. Hollow fibers can be obtained, for example, from Spectrum, Inc., Laguna Hills, California / USA and the Hoechst Celanese Company. A preferred method according to the invention for embedding the fibers in the tube disks includes the regular alignment of a fiber bundle, as well as the subsequent, joint fixing of the individual fibers in a deep bed made of a thermoplastic or thermally curable but already cured polymer, such as a polyurethane. Another bed made of a curable polymer is used to maintain a certain distance ( 11 in Figure 3) along the length of the fibers from the first bundle. The outer surface of a flat tube disc can thus be produced by cutting through a bundle fastened in this way perpendicular to the fiber axes. A cut can then be made through the other, fixed bundle at a suitable distance from the first outer surface, in order thus to produce the second outer surface. Finally, the tubular bundle with the tube disks can be glued to the ends of an elongated housing or sealed in some other way so that a module can be obtained. The method which is suitable for use in the context of the present invention for producing modules which contain untreated hollow fibers, that is to say fibers without a non-porous, extremely thin, gas-permeable layer, is well known to those skilled in the art. Modules containing a variety of uncoated hollow fibers are commercially available and sold by various manufacturers such as Spectrum, Inc. and Hoechst Celanese.

The practical implementation of the novel method for coating hollow fibers can be understood by referring to FIG. 3. In the case of a cylindrical module 30 based on uncoated hollow fibers, the cavities on the tube side are provided with the covers 31 and 32 . These covers have the connections 31 a and 32 a in order to conduct fluids into the tube-side cavity and also out of this cavity. In the context of the embodiment shown here, the module is placed in an upright position so that the longitudinal axes of the essentially parallel hollow fibers 33 are aligned vertically. It has been found that this upright orientation of the fibers is preferred in order to achieve the required result of a uniformly thin coating on the inside of the fibers. The connection of the module arranged in the foot region of the line is connected to a storage container 34 via the supply line 36 . The pump 37 is used to pump polymer solution out of this reservoir through the tube-side cavity. An excess of fluid that occurs in the interior of the line is passed back from the connection 32 a arranged in the upper region of the line through the disposal line 38 and the regulating valve 40 into said storage container. Usually, the connection 7 b arranged in the upper region of the sleeve-side cavity is either closed with a blind line (not shown) or with a valve 35 . In addition, fluid originating from the sleeve-side hollow space is also returned to the storage tank via the overflow line 39 .

The polymer solution is pumped from the container 34 through the tube-side cavity of the module 30 in the form of a circuit back to the said container by means of the pump 37 . The regulating valve 40 is set so that a slight pressure is exerted on the tube-side cavity. This pressure forces the solvent to pass through the microporous hollow fibers, causing the build-up of a layer of gas permeable polymer on the inner surface of the fibers. As soon as the build-up of this polymer layer has progressed to a predetermined thickness, the circulation-like passage of the polymer solution is terminated and the entire fluid is drawn off from the tube-side and sleeve-side cavities. Finally, a gas purge with a high gas flow is carried out through the side line in order to remove all remaining solvent residues.

Initially, a dilute polymer solution is first prepared by working in a suitable solvent dissolves a gas-permeable polymer. As part of a The possibility to carry out the procedure in practice will be necessary in advance Amount of polymer and solution based on the required thickness of a coating of the tube-side area calculated. This means that the total surface area of the Gas filter using the dimensions of the hollow fibers used and the details of the Manufacturer of the modules is calculated. Then you can change the amount of polymer calculate which is required to produce a given thickness of the coating. Then a storage container is loaded with a solution that is at least the calculated one Contains amount of polymer. The actual thickness of the coating can be seen after completion empirically determine the method.  

The description of the method given in the preceding text relates to the coating of the inner surfaces of hollow fibers with gas-permeable polymer. However, coating the outer surfaces of such fibers is also considered to be another embodiment of the present invention. The apparatus shown in FIG. 3 can also be used to coat the outer fiber surfaces by passing the polymer solution through the sleeve-side cavity in the manner of a cycle. This can be achieved by pumping the solution into the connection 7 a arranged in the lower region of the sleeve-side cavity and then pumping it out again through the valve 35 from the connection 7 b arranged in the upper region of the sleeve-side cavity. In a comparable manner, the connection 32 a in the upper cover of the line is converted into a dummy line, or the valve is closed, and the solvent which has penetrated through it is passed back into the storage container through the connection of the cover 31 a arranged in the foot region of the line. The lines 36 , 38 and 39 and the pump 37 are each connected in a suitable manner with the correct openings in order to achieve the desired, circulation-like passage of the fluid.

One can use a gas filter module based on hollow fibers, in the context of which the fibers in each case on its inside of the tube according to the present invention with one of a gas-permeable polymer existing layer are provided in the following use the described method. For example, you can add an aerosol cause to flow through the tube-side cavity. For this, a appropriate aerosol source connected to the input port of the line so that it the aerosol is able to reach the entrance cover, the coated Pass the interior of the hollow fibers, then through the outlet cover of the module Leave the line again and finally afterwards through the one intended for the aerosol Outlet port to get into a collection container. The outlet connection of the line can be completely closed, so that the tube-side cavity either becomes a Dummy line is converted, or at least partially blocked. So it becomes clear that the filtered gas component by the consisting of the amorphous copolymer Coating travels through, so that finally the filtered gas exits the outlet port of the sleeve-side cavity reached to be collected there.  

It must also be noted at this point that both in the manner of practical work with the module elements according to the present invention, as well as what Number, external shape and placement of said module elements, a variety of Variations are possible, all of which are within the scope of the present invention can be used.

For example, the non-porous layer consisting of amorphous copolymer can also be applied the outer surface of the used, oriented towards the sleeve-side cavity Hollow fibers are arranged. In this case, the aerosol should preferably pass through the sleeve-side cavity of the module flow while the filtered gas through the tube-side cavity should flow. The connection provided for derivation can also used to collect accumulated solids or precipitated liquid remove, since after a certain period of time a significant amount of such Materials are filtered out of the aerosol.

Preferred applications for teaching the present invention include Providing uncontaminated gas in an environment that has clean rooms corresponds to how they are common in the production of microelectronic components, also the filtration of engine exhaust gases and the filtration in the context of process plants that process biological material. You can do that also use novel gas filters to remove finely divided, contaminating substances from exhaust gases to separate, which arise in the course of carrying out chemical processes, before one releases such gases in the atmosphere.

This invention will now be illustrated in more detail with the help of examples, each of which represent certain typical embodiments, all of which relate to parts, Quantities and percentages related to weight are unless expressly stated otherwise. If not stated otherwise is, or the opposite is directly apparent from the context, all are in the text specified pressures based in each case on the atmospheric pressure. Originally not in Forms of SI information available weight and dimensions were each in SI Converted units.  

EXAMPLES

Materials used in the examples described below include the following:
Polymer A: Teflon® AF 2400 (EI du Pont de Nemours and Co., Wilmington, Delaware / USA), a dipolymer consisting of 85 mol% perfluoro-2,2-dimethyl-1,3-dioxole and 15 mol % Tetrafluoroethylene with a glass transition temperature of 240 ° C;
Polymer B: Teflon® AF 1600 (EI du Pont de Nemours and Co., Wilmington, Delaware / USA), a dipolymer consisting of 65 mol% perfluoro-2,2-dimethyl-1,3-dioxole and 35 mol % Tetrafluoroethylene with a glass transition temperature of 160 ° C;
E-PTFE expanded polytetrafluoroethylene;
O-1 SAE 10W-30 automotive engine oil from Quaker State;
O-2 vacuum oil from Norton Petroleium Co., Newark, Delaware / USA

Example 1 and Comparative Examples 1 to 4

A 0.025% by weight coating solution of Polymer B in FC-75 was prepared. Approximately 8.9 cm x 20 cm of a microporous, rectangular E-PTFE film, obtained from WL Gore and Associates, Elkton, Maryland / USA with the designation Goretex® No. X19290-BAG 10F2 and a nominal pore size of 0.05 µm were placed on a clean glass plate with the narrow side in the 12 o'clock position (located above). The thickness of the E-PTFE film was approximately 127 µm. The film was attached to the plate using a pressure sensitive adhesive tape placed along the top edge. The film was then placed in a clear box which was flushed with gaseous nitrogen to minimize the risk of contamination during coating. FC-75 was placed on the film until it was saturated. Excess solvent and possible air pockets were removed by pulling a rubber roller squeezer from top to bottom over the entire film under slight pressure. Then some coating agent in the form of a bead was placed on the film in the region of the upper film edge, and a doctor blade with a depth of 254 μm was drawn continuously from top to bottom over the film surface. After that, the coating was left at room temperature for one hour to dry. The coated film was then placed in a vacuum oven at 50 ° C. for 15 hours and at 10 cm ³ / min. flushed with gaseous nitrogen.

A portion of the uncoated E-PTFE film (Comparative Example 1) was then placed in a holding device for membranes, and this film was used to separately measure the permeability rates of oxygen and nitrogen. The O ₂ / N ₂ selectivity was calculated based on the gas flow measurements shown in Table I. The gas flow and the selectivity of the E-PTFE film coated with polymer B (comparative example 2) were determined in a comparable manner. Then the two oils O-1 and O-2 were each deposited separately on samples of the films according to the two comparative examples 1 and 2, essentially in accordance with the procedure which was incorporated in the present disclosure by this reference Chapter "Visual Oil Wetting" of US Pat. No. 5,116,650. The wetting characteristics of the samples were observed in accordance with the results described in Table II, although the samples were not touched. Before contact with the oil, the foils had a uniform, light color. The wetting of the films could be determined by visual inspection and was shown in the area of the wetted film surface in the form of a discoloration of the film to a contrasting, gray color. After 24 hours, the wetted surface of the samples to be examined was tilted to an angle of 45 ° to the horizontal. The tendency of the oil drops to roll down the resulting inclined plane was then observed, as a result of which the film could be wetted by the oil. A 0.01 weight percent solution of Polymer A in FC-75 was also prepared. The solution of polymer A was used to coat a fresh, rectangular piece of film made of E-PTFE (comparative example 3) in the same manner as described in comparative example 2.

Using a 0.2 weight percent solution of Polymer A that was used to make a made of microporous polysulfone, from Memtec in San Diego, California / U.S.A. The procedure was then to coat the produced film repeated to produce the coated, flat films. The porosity of the polysulfone Substrate corresponded to a MWCO value of 100,000. As in the previous text  the selectivity and oil wettability of the uncoated Polysulfone substrate (Comparative Example 4) and the coated polysulfone (Example 1) certainly.

In the context of Comparative Examples 2 and 3, a gas flow, which was determined separately in each case and was lower than the corresponding values of Comparative Example 1, indicated that the coating on the PTFE film somewhat reduced the pore size of the substrate. Nevertheless, the fact that the selectivity for O ₂ and N _{2 remained} close to the number one led to the conclusion that the pores remained open even after the substrate had been coated. The two polymers A and B each have a high O ₂ / N ₂ gas selectivity. Example 1 shows that the gas permeability of oxygen is about twice the numerical value compared to nitrogen, it also being possible to verify that the polysulfone coating is non-porous and has been applied continuously to the entire substrate.

Table II shows that the non-porous membrane of Example 1 against wetting is considerably more resistant due to oil than with the porous, coated E-PTFE structures the case is. Coating the E-PTFE material thus improved the resistance against wetting by oil compared to the uncoated E-PTFE films (Comparative Example 1). However, after placing oil on the substrate of the comparative example 2 had applied, this drop began to clog the membrane within a few minutes wet what could be demonstrated by a spreading, gray spot. The sample according to Comparative Example 3 was found to be more resistant to wetting through oil, but after taking the sample over a period of 3.25 hours with the oil a measurable area under the drop was wetted in this case too. The non-porous coating of polymer A (Example 1) resulted in comparison with the Results of Comparative Example 4 on a dramatically improved resistance to wetting with oil. In this case, none could continue after 3.25 hours visible evidence of wetting can be determined. In addition, in the cases of Non-porous coated polysulfone samples unhindered down the oil drops as soon as the flat structure, while the oil drops at the most stable, do not set the porous coated E-PTFE sample at all. Even after After 168 hours, the material of Example 1 was still found to be stable against the oil drops. This behavior also shows that the non-porous coating  Membranes are considerably more resistant to wetting with oil than the state of the art Technology are common structures.

Table I

Table II

Example 2

16.38 g of polymer A was placed in a glass bottle containing 900 ml (1620 g) FC-75. The bottle was sealed, shaken by hand for about 10 minutes and then placed on a roller mill under a hot lamp overnight. In this way, a base solution containing 1% by weight of polymer A was obtained. Then, by adding 810 ml of FC-75 to 90 ml of this 1% by weight base solution in a clean glass bottle and then shaking the bottle by hand for about 5 minutes, a 0.1% by weight coating solution could be obtained. This dilution of the base solution was carried out repeatedly in order to have a sufficient supply of coating solution available. Then a standard "Krosflo" type hollow fiber module (manufactured by "Spectrum, Inc., Laguna Hills, California / USA, Article No. K25S 100 01N) with a polysulfone housing with an inside diameter of 6.35 cm and about 5087 was used Hollow polysulfone fibers, each with an inside diameter of 460 µm and an outside diameter of 640 µm, and a pore size that corresponded to a MWCO value of 50,000), underwent a conversion by the manufacturer, which involved removing the finger nets on the connections in the area of the sleeve-side cavity exist. the total length of the fibers was 22.86 cm, wherein the effective Laene cm was 19.05. This converted hollow fiber module was placed in a vertically oriented position, substantially coincident with the representation in FIG. 3. the terminal 7 b in the upper area of the sleeve-side cavity was converted into a dummy cable and thus closed. The end sections of the fiber module were checked covers attached. The top and bottom side pipe connections 31 a and 32 a with a nominal diameter of 3.8 cm as well as the connection 7 a in the lower area of the sleeve-side cavity were narrowed with the help of tubular barbed adapters to the extent that they had a Platinum-hardened, made of silicone rubber line with an inner diameter of 79 mm. A "Masterflex L / S Quickload" peristaltic pump, which was operated with the aid of a motor, the speed of which could be regulated in the range from 6 to 600 revolutions per minute, was placed at a distance of approximately 15.25 cm below the Foot area of the line arranged connector 31 a placed. Conduit material made of silicone rubber was used to connect the module and the pump to 40038 00070 552 001000280000000200012000285913992700040 0002019882417 00004 39919 each with a storage container with a capacity of 2 liters, whereby a container made of low-density polyethylene material than that shown in the context of FIG. 3 Storage container served.

Originally, said storage container was charged with 1800 ml of the 0.1% by weight coating solution. The pump was then started to establish a flow out of the reservoir into the connection of the module arranged in the foot area of the line. The upper and lower fiber ends within the module could be observed visually through the transparent covers. The flow rate was adjusted so that a period of 15 seconds elapsed between the time the solution first flowed into all of the fibers and the overflow of the solution at the upper fiber ends. After the level of the solution in the reservoir dropped due to the filling of the module, the reservoir was additionally charged with another 400 ml of coating solution. After a flow was established from the upper ends of the lines, a flow was drained from the port in the lower portion of the sleeve-side cavity at certain predetermined times, and the time required to collect 25 ml of the permeate was determined . The flow through the disposal line 38 was regulated by loosening or tightening the hose clamp 40 as appropriate, with the requirement in each case to keep the period within a range of 8 to 15 seconds, that of collecting 25 ml of permeate was required. The data actually measured, together with the corresponding collection times, are shown in Table III.

Table III

The viscosity of the permeate was determined using a technical glass product, Inc., (Dover, New Jersey, U.S.A.) manufactured serial number 191 ("cross arm" type) measured. When using a standard amount of permeate, the The time it took for the permeate to flow completely through the viscometer 225.66 seconds. In contrast, a 0.1% by weight solution of polymer A requires 325 Seconds to flow through the same viscometer. These measurements confirm that the permeate is substantially free of polymer dissolved therein, and that the microporous substrate effectively removes the polymer from the Filtered out polymer solution. After a circular circulation of the solution with a The pump was switched off for 10 minutes. The supply line was then clamped below the lateral line connection with an artery clamp and severed below this artery clamp. Even those from the top, from the side Line connection outgoing line was cut off. Then the module was tilted around the permeate from the sleeve-side cavity and into the storage container to lead. The polymer solution still present within the tube-side cavity was placed in a clean beaker by removing the artery clamp afterwards  removed. Then the module was aligned vertically again and it became one Supply line connected to the upper, lateral line connection through which gaseous nitrogen could be introduced under low pressure. Then the tube-side cavity of the module for a period of 5.5 hours at one Flushed at a rate of 30 l / min with gaseous nitrogen. It also became certain, randomly selected points in time the module is temporarily tilted, around any liquids accumulated within the sleeve-side cavity empty.

The thickness and gas selectivity of polymer A on the fibers were determined in the following manner, respectively. First, the permeability of the pure gases through the polymer A was determined with the help of corresponding tables prepared beforehand. This tabulated data could be obtained from measurements of the flow rate of pure gases through monolithic monolithic membranes of uniform thickness made by the method prepared in accordance with the method described in U.S. Patent No. 5,051,114, which Literature is to form part of the present disclosure based on the corresponding reference. One of the two connections in the upper area of the tube-side cavity and one of the two connections in the area of the sleeve-side cavity were closed in each case. A gas stream consisting of pure gas at a temperature of 25 ° C. and a slight excess pressure was then passed in via the open connection in the region of the tube-side cavity. This gas flow was allowed to penetrate through the coated hollow fibers, and the gas flow was then passed into a calibrated burette via the open connection as it left the sleeve-side cavity. On the basis of the known data on gas permeability, the filter surface size of the module and the speed of the gas flow, it was possible to calculate that the average thickness of the coating on the hollow fibers corresponded to a numerical value of 0.1 µm. These flow rate measurements were carried out separately with pure oxygen and pure nitrogen. The O ₂ / N ₂ selectivity could then be calculated on this basis by dividing the flow rate of oxygen by the flow rate of nitrogen, giving a numerical value of 1.90. This example thus demonstrates a method for coating the entire filter surface of hollow fibers with an extremely thin layer consisting of an amorphous polymer.

Example 3

A 0.025% by weight coating solution of polymer A was prepared adding 877.5 ml of FC-75 to 22.5 ml of that in the example in a clean glass bottle 2 base solution prepared and shaken by hand for five minutes. This dilution of the basic solution was repeated in order to make it sufficiently large To have a supply of coating solution available.

Then another "Krosflo" type hollow fiber module used in Example 2 was installed in a vertical position. The module 41 was connected to a system suitable for the circulation of solution, as is shown schematically in the context of FIG. 4. The pump and reservoir were each identical to the equipment used in Example 2. The upper connection in the area of the sleeve-side cavity was closed again by converting it into a dummy line. By contrast, the lower connection of the side shell was connected by means of line 42 to a filter piston 43 of the KIMAX type, which had a capacity of 1000 ml. The vapor space of this filter flask was sucked off with the aid of a vacuum source (not shown) via the disposal line 44 , the vacuum source consisting of a two-part vacuum trap immersed in ice with a length of 36.8 cm and an inner diameter of 3.8 cm and a conventional laboratory -Vacuum pump of the type "Welch Duo-seal" existed. Air could be blown into this vacuum trap via a (not shown) adjustable valve, so that a targeted control of the pressure prevailing in the filter piston was possible.

The said storage container was originally charged with 1800 ml of coating solution. The pressure prevailing in the filter flask was set to an absolute numerical value of 7.5 cm of mercury. Then the solution circulation pump was started to build a flow into the foot of the module. The flow rate was adjusted by means of a corresponding inspection by eye so that a period of 15 seconds elapsed until all of the fibers were filled with the solution. The permeate then began to accumulate inside the filter flask. After the level of solution in the storage container had successfully dropped and additional space had been created, the storage container was filled with another 700 ml of coating solution. As in the context of Example 2, the viscosity of the permeate was also measured here, which turned out to be identical to the viscosity of FC-75. One hundred and five seconds after the fibers had been filled, the pressure was adjusted so that the vacuum in the filter flask corresponded to an absolute numerical value of 3.8 cm of mercury. Two hundred and ten seconds after the fibers were filled, the reservoir was emptied and the pump for solvent circulation was switched off. The module was then separated from the solution apparatus and the existing liquid was drained. The fibers were then dried in a gaseous nitrogen stream which, as in the context of Example 2, at a rate of 30 l / min. Was flushed through the tube-side cavity for 5.5 hours. On the basis of the measurement methods described in Example 2, it was found that the average thickness of the polymer A layer on the hollow fibers was 0.1 μm, while the O ₂ / N ₂ selectivity corresponded to a numerical value of 1.84.

Examples 4-6

The procedure described in Example 2 for coating the inner surface of hollow fibers was repeated, but with the modifications described below. A Spectrum-type hollow fiber module with a diameter of 2.54 cm and the number M15S260 O / N and about 361 fibers and an effective length of 14.2 cm was used, which had an overall filter surface area of 680 cm ² . The gas flow of oxygen and nitrogen and the selectivity of the membranes were determined in each case, the data obtained in this way being summarized in Table IV. These examples demonstrate that the teaching of the present invention can be used to produce a gas filter with an overall small cross-section, which has a continuous, extremely thin layer of a gas-permeable membrane and thus enables a considerable gas flow.

Table IV

Example 7 and Comparative Example 5

The cylindrical module, corresponding to reference number 55 in FIG. 5 and based on coated hollow fibers according to example 4, was connected to a testing apparatus shown in FIG. 5 (example 5). Overall, the cross-sectional area of this module based on the cylinder diameter Dhf was 5.1 cm ² . The filter surface of this module was 680 cm ² . A centrifugal pump 80 was equipped with the oil device 82 , which consisted of a wick immersed in a container with the oil O-2. Said wick was connected to the suction side of the pump, which resulted in oil droplets being suspended in the air 83 flowing out of the pump. Thus, air was taken up as a result of the suction effect of the pump and blown off by means of the valve 51 through the line 54 into the environment. A certain proportion of the oil-enriched air was discharged by means of the manually controlled valve 52 and transferred into the holding device 60 for membranes in the form of flat films. An excess of oil-enriched air was drawn off from the said membrane holding device by a corresponding line provided with the manually controlled valve 62 . Air which had already penetrated through the membrane arranged in the holding device was disposed of with the aid of line 64 , which was intended to be connected to the foot region of a glass, calibrated cylinder (not shown). Soap solution was introduced into this calibrated cylinder in order to volumetrically determine the flow rate of the permeate using the bubble expansion technology customary in the prior art. Another part of the pumped air was diverted by means of the manually controlled control valve 53 into the upper region of the line of the sleeve-side cavity of the fiber module 55 . An excess of oil-enriched air flowed through the lines and was discarded through a line provided with the manually controlled valve 56 . Both from the upper and from the lower connection in the area of the sleeve-side cavity, the air that had penetrated through the module was disposed of with the aid of the common valve 57 , which was also designed in such a way that it could be connected to a measuring cylinder that measures the gas flow with the help of the soap bubble expansion.

In the context of Fig. 6 is a cross section illustrating the schematic view through the holding device 60 for circular membranes in the form of flat sheets having a diameter Dfs of 47 mm, which is manufactured by Millipore Corporation, Bedford, Massachusetts / USA. Overall, the cross-sectional area of this membrane holding device in the form of flat films was 17.3 cm ² , the total filter surface area of the membrane being 9.6 cm ² . The holding device has an upper block 61 and a lower block 63 , which are each designed such that they can include a gas-permeable membrane 65 and a rigid perforated plate arranged on the rear side thereof. The lower block is also processed so that a channel 77 is defined inside the block. The gas to be filtered was fed through the inlet opening 68 . All connections were provided with connecting lines (not shown). The incoming air moved towards the membrane in the direction of the arrow. The air was introduced into a narrow cavity located directly next to the membrane and collected in an outlet duct 72 , from where it could be disposed of through the connection 69 . The air that had already passed through the membrane was removed from the cavity 71 by means of the connection 70 in the direction of the arrow. This air, which had already passed through the membrane, was separated from the incoming air with the aid of the membrane and an O-ring 67 consisting of an elastomer.

A circular cutout with a diameter of 47 mm from the coated membrane of Comparative Example 2 was placed in the holding device for membranes in the form of flat foils, the coated side being directly exposed to the gas entering (Comparative Example 5). Then the pump 80 was turned on, causing an oil-enriched air flow to flow through the valve 51 to the position 54 . Excess oil disposal valves 56 and 62 were closed. The manually controllable valves 52 and 53 were opened in order to direct the oil-enriched air onto the membrane in the form of a flat film or into the hollow fiber module. The valves were set so that the gas through each of the disposal lines 64 and 57 at a rate of 2 l / min. flowed through. From time to time the pressure indicated on the two pressure gauges 58 and 59 was read and noted together with the corresponding results of the measurement of the gas flow. In this experiment, the novel gas filter and a membrane according to the prior art in the form of a flat film were thus exposed to a gas which had the same concentration of oil. Table V summarizes the data obtained in the course of this experiment.

Table V

The data compiled above show that the membrane flat film applied pressure difference stable over a period of about 90 hours stayed and then rose quickly. After 121 hours the membrane was in Form of a flat film essentially completely clogged. The gas flow through the The membrane in the form of a flat film started after about 68 hours To show signs of easing. After 121 hours, it almost dropped to zero from. Immediately after the start of the test, the one on the coated one rose Hollow fiber module gradually applied pressure difference. Originally it was on that Hollow fiber module applied pressure difference greater than that on the flat film, such as this is the case with a continuous, non-porous gas flow barrier compared to one porous membrane would also expect.

After approximately 89 hours, air began to be vented through valves 56 and 62 , which are provided for excess oil-enriched air, for five minutes. This measure was carried out in order to attempt to clean the gas filter of any oil that may have accumulated in it. In the course of these "blow-out steps", no liquid oil could be removed from the holding device for membranes in the form of flat foils, whereas liquid oil did flow out of the fiber module. These findings suggested that while the oil could pass through the flat membrane unhindered, the hollow fibers could not. The module had a transparent housing. By visual inspection during the test it could be shown that no liquid oil penetrated the fibers, so that no oil could collect in the cavity on the sleeve side. However, when the said holding device for flat films was opened after the end of the investigation, liquid oil could be found both in the membrane and on the upwardly oriented surface of the membrane. These findings confirm the assumption made above with regard to the passage of oil through the membranes.

The blowing out of air through the excess oil-enriched air provided lines resulted in the gas flow in each of the two gas filters was immediately reset to the setpoint of 2.0 l / min. This flushing process was then repeated five more times. After four of these processes, each was found a significant increase in gas flow through the hollow fiber module. The In contrast, a membrane in the form of a flat film did not react at all to any of the subsequent rinsing processes. In the case of the hollow fiber module, the flow remained on urgent air for more than 168 hours at a value that is more than 50% of the original setpoint was set. As the investigation after the lapse of 213 hours was ended, the gas flow in the case of the hollow fiber module was 46% of the target value. Also the pressure drop that occurred after passing through the hollow fiber module was lower than that corresponding difference in pressure measurements in the case of the membrane in the form of a flat Foil. These data demonstrate that the novel membrane has a continuous, non-porous barrier in the form of a gas permeable membrane against an oil triggered, possible constipation is stable for a significantly longer period than this is the case with a porous membrane. You can also use a non-porous one Membrane up to the original gas flow by repeated cleaning Regenerate to initial strength.

Example 8 and Comparative Example 6

A sample of a freshly produced, porous membrane according to Comparative Example 3 with a diameter of 47 mm was installed in a holding device for membranes in the form of flat films (Comparative Example 6). Ports 68 and 69 ( Fig. 6) were closed and oil O-2 was poured into port 70 to fill the interior of the holder. Similarly, valve 56 ( FIG. 5) of the hollow fiber module was closed in accordance with Example 6, and the tube-side cavity of the module was also filled with oil O-2. The gas filters were left in this liquid-filled state for one hour. The oil was removed from the gas filters that had been installed in the test apparatus according to FIG. 5. Excess air valves 62 and 56 were opened and pump 80 was turned on. The gas filters were flushed with air for 10 minutes to remove oil residues. Then valves 62 and 56 were closed again, and valves 51 , 52 and 53 were adjusted so that a controlled pressure of 5 lbs _f / in ² could be set using manometers 58 and 59 . The data obtained in this experiment are summarized in Table VI.

Table VI

This experiment demonstrates that the novel membrane with a continuous, non-porous layer of an oleophobic, gas-permeable polymer compared to one with the same polymer coated, microporous structure with an improved Resistance to possible wetting by oil. The gas flow through that novel hollow fiber module proved to be high and also remained over a period of stable for more than 24 hours. The membrane customary in the prior art was against this clogged after less than three hours.  

Example 9

A 0.1% by weight base solution was prepared by adding 1.164 g of polymer B into a glass bottle with 900 ml (1620 g) FC-75 and then shaking this glass bottle by hand for about 10 minutes. This solution was then mixed vigorously by heating the said bottle overnight under a suitable lamp and at the same time rolling back and forth on a roller mill. Then a 0.005% by weight coating solution was prepared by diluting 50 ml of said base solution with 950 ml FC-75 in a clean glass bottle and shaking for five minutes. This dilution of the base solution was repeated to prepare 4 liters of the coating solution.

An approximately 1,153 microporous polysulfone fibers with an inner diameter of 460 μm and an outer diameter of 640 μm, having the “MiniKros” type hollow fiber module (manufactured by “Spectrum, Inc.”, component number S555 001 HF-2) with a polysulfone housing, the Was 3.2 cm, was installed in a coating apparatus corresponding to that shown in FIG. 4, but horizontally. A porosity corresponding to a MWCO value of 50,000 was determined for the polysulfone fibers. The effective length of the polysulfone fibers was 20 cm, resulting in a total filter surface area of 3895 cm ² . The pump and reservoir were each identical to the equipment used in Example 2. The two connections of the side shell were made using a "Y". - Connected like configuration, lines made of silicone rubber, and the common line was then connected again to a filter flask of the KIMAX type, which had a capacity of 1000 ml. The vapor space of this filter flask was sucked off with the aid of a vacuum source (not shown) via the disposal line 44 , the vacuum source consisting of a two-part vacuum trap immersed in ice with a length of 36.8 cm and an inner diameter of 3.8 cm and a conventional laboratory -Vacuum pump of the type "Welch Duo-seal" existed. Air could be blown into this vacuum trap via a (not shown) adjustable valve, so that a targeted control of the pressure prevailing in the filter piston was possible.

The said storage container was originally charged with 1800 ml of coating solution. The pressure in the filter flask was reduced to a vacuum corresponding to an absolute Numerical value of 30 cm of mercury set. Then it became a solution circulation provided pump started to flow the coating solution into the module build up. The permeate then began to accumulate inside the filter flask. After the level of solution within the storage container has dropped sufficiently and additional space was created, the storage container with a further 1,700 ml Coating solution loaded.

The filter flask was filled three minutes after the recirculation of the solution began. So that an empty piston could be installed, a valve in the vacuum line (44, cf. FIG. 4) was temporarily closed. The valve was then opened again and the filtration could begin again. Such an exchange of the filter flask was repeated again 7 minutes and 11 minutes after the start of the experiment. After 14 minutes, the reservoir was empty and the solvent circulation pump was turned off. The module was then separated from the solution apparatus and the existing liquid was drained. The fibers were then dried in a gaseous nitrogen stream which, as in the context of Example 2, at a rate of 30 l / min. Was flushed through the tube-side cavity for 5.5 hours. As in the context of Example 2, the viscosity of the permeate was then measured here, which turned out to be identical to the viscosity of FC-75, that is, it was determined by a dropping time of 225 seconds through a viscometer of type No. Given 191. On the basis of the measurement methods described in Example 2, it was found that the average thickness of the polymer B layer on the hollow fibers was 0.45 μm, while the O ₂ / N ₂ selectivity corresponded to a numerical value of 2.59.

Example 10

A hollow fiber module was coated as described in Example 9, but with the following modifications. A 0.5% by weight coating solution of the Polymers A used. The coating solution was prepared by adding 500 ml added 500 ml FC-75 to the base solution prepared in Example 2 and this Mix the mixture by hand for about five minutes.  

The hollow fiber module used was an approximately 1,000 microporous polypropylene fibers with an inside diameter of 200 µm and an outside diameter of 250 µm, having the "MiniKros Sampler" type hollow fiber module (manufactured by "Spectrum, Inc.", special version with the Number 032596-1) with a polysulfone housing, the inside diameter of which was 1.6 cm. The nominal pore size of the polypropylene fibers was 0.05 µm. The reservoir was charged with 500 ml of coating solution and the pressure in the filter flask was adjusted to a vacuum corresponding to an absolute numerical value of 5 cm of mercury. The module was then installed vertically oriented in the apparatus for circulating the solution. The solution circulation pump was then started to build up the flow of the coating solution into the base of the module, specifying a speed that would fill the lines in 4 seconds. After the coating solution was circulated for 9 minutes and 15 seconds, the pump for solvent circulation was turned off. The module was then disconnected from the circulation equipment and the existing liquid was drained. The fibers were then dried in a gaseous stream of nitrogen at a rate of 1 l / min. Was flushed through the tube-side cavity for 5.5 hours. The thickness of the non-porous polymer layer on the inside of the fiber was then also measured for this coated module, a numerical value of 0.9 μm being determined, while an O ₂ / N ₂ selectivity could be measured according to a numerical value of 1.81.

Example 11

There was a hollow fiber module on the respective outside of the fibers, that is, on the Coated side of the fiber outer skin. The procedure was the same as that of the example 10 comparable to that in this case too, the coating solution is passed through under vacuum the hollow fibers were sucked through. It was for the coating solution as a whole 200 ml of a 0.1% by weight base solution of polymer B used as described in Frame of Example 9 was made. It became an approximately 1'190 microporous Polypropylene fibers with a pore size of 0.05 µm and an effective length of 21.3 cm hollow fiber module of the "MiniKros Sampler" type (manufactured by the company "Spectrum, Inc.", special design with the number 081696-2) used the horizontal  oriented into the apparatus for the circular circulation of the solution. The Coating solution was introduced into one of the connections of the side shell and over the another connection of the side shell back into the reservoir. The two Lateral pipe connections were made using a "Y" shaped connector linked together, and the common management was combined with that for collecting the Permeates connected to pistons provided within the vacuum system. So that was FC-75 out of the solution on the sleeve-side cavity and through the microporous Fibers sucked into the inside of the fibers. The vacuum in the tube-side cavity was set so that the prevailing pressure was an absolute numerical value of 500 mm Mercury column corresponded.

The cycle-like circulation was terminated as soon as the reservoir was emptied. The module was then disconnected from the circulation equipment and the existing liquid was drained. A stream of nitrogen was passed at a rate of 8 l / min. Flushed through the bowl side for 20 minutes. In order to continue drying, an additional stream of gaseous nitrogen, also provided for drying, was then added at a rate of 0.5 l / min. Flushed through the shell side for 8 hours. After coating, the coating thickness was also measured for this module, a numerical value of 0.3 μm being determined, while an O ₂ / N ₂ selectivity could be measured corresponding to a numerical value of 1.72.

Example 12

It became a hollow fiber module made of about 99 microporous polyvinylidene fluoride ("PVDF") existing hollow fibers, coated with the polymer A, namely in essentially in the same way as described in Example 2 but with the following modifications: a module of the type "Krosflow" (manufactured by "Spectrum, Inc.") with the serial number S555001HF-12 with a Inner diameter of 1.6 cm used. The fibers had an inside diameter of 1.0 mm and an outer diameter of 1.2 mm, with a pore size accordingly a MWCO value of 500,000 was determined. The total length of the fibers was 13.6 cm, and the effective length 12.5 cm.  

The module was made horizontal using cables made of silicone rubber oriented in the apparatus for the circular circulation of the solution built in by everyone of the connections on the shell side, which in turn with the help of a "Y" - shaped connector were linked together. Instead of the permeate in the Returning the reservoir was made by this "Y" shaped connector outgoing, common disposal line connected to a collecting bottle. The Storage containers with a capacity of 1 l were charged with 200 ml of coating solution. The pump was operated at a flow rate of about 5 ml / sec. The Return line that comes out of the outlet in the area of the tube-side cavity led the storage container back, was with the help of a hose clamp on one Cross-section set, the reflux of about 3.5 ml / sec. allowed. In this way about 1.5 ml of permeate was collected per second. The pump was turned off as soon as the reservoir was emptied. The existing within the module Liquid was drained and a stream of nitrogen was depressurized at a low pressure Speed of 2 l / min. Flushed through the tube-side cavity for 4 hours.

After coating, the coating thickness was also measured for this module, a numerical value of 2.70 μm being determined, while an O ₂ / N ₂ selectivity could be measured corresponding to a numerical value of 1.87.

Although for purposes of illustration in the drawings and examples certain embodiments of the invention have been selected and the previous Description is limited to certain technical embodiments to this This description is intended to describe specific embodiments of the invention by no means the scope of protection of the present defined with the help of the claims Limit invention in any way.

Comparative Example 6

Using the procedure described in Example 9, a module with 12 hollow fibers and a filter surface area of 11.5 cm ^{2 was provided} on the inside of the fibers with a layer made of the polyimide polymer manufactured by the company Ciba-Geigy with the name "Matrimid 5218" existed. The hollow fibers in question were microporous polypropylene with a porosity of approximately 0.05 μm, which corresponds to a MWCO value of approximately 100,000. The polyimide had a molecular weight of 30,000 and, in N-methylpyrrolidone, a logarithmic viscosity number ("inherent viscosity") of 0.6. The polymer was dissolved at a concentration of 1.5% by weight in clear dimethylformamide, whereby 100 ml of an orange-colored coating solution could be obtained. The coating solution was drawn through the fibers under a vacuum which corresponded to an absolute pressure of about 380 ml of mercury. It was observed that the permeate liquid was colored orange, which is an indication that the polymer could not be effectively filtered by the microporous hollow fibers used.

Both nitrogen and oxygen each had a gas flow of around 65,000 GPU through the uncoated module. After coating, both the gas flow of nitrogen and that of oxygen were reduced to a numerical value of 14,700 each. The O ₂ / N ₂ selectivity remained approximately one, indicating the fact that no continuous, non-porous layer of a gas permeable polymer had been formed on the polypropylene substrate. Non-porous polyimide has an O ₂ / N ₂ selectivity that is greater than 5.0. This example demonstrates the importance of relating the molecular weight of the dissolved polymer and the pore size of the substrate so as to enable the substrate to filter out the polymer in such an effective manner that it results in a continuous non-porous layer can be obtained according to the present invention.

Examples 13-14 and Comparative Examples 7-8

There were four modules, the construction of which in the context of Examples 4 to 6 was comparable on the inside of the polysulfone hollow fibers corresponding to that Method of this invention each with extremely thin polymer A consisting Provide layers. The relevant data are given in Table VII compiled. The main difference between these examples is that in the context of the comparative examples, the solvent by drying in a vacuum oven was withdrawn overnight and at a temperature of 100 ° C, while in contrast  Within the scope of the exemplary embodiments overnight with the flow rate specified in each case gaseous nitrogen was purged.

Based on the measured flow through the fibers and the known permeability of the Coating composition, the average coating thickness was calculated. The average inner diameter of the fibers used was determined using hydraulic Calculations measured based on the measured flow at a measured pressure drop based on the entire line arrangement. The uncoated fibers had one average inside diameter of 420 µm. These data show that regardless of the very thin coating, which in all cases was much thinner than 1 µm, the middle Inner diameter of the fibers in the hollow fiber modules of the comparative examples considerably was smaller than the expected dimensions in the range of about 418 µm. One can assume that the difference is due to the non-uniform thickness of the coating Fiber inner sides decreases. If the solvent comes through a gas flush high flow rate was removed, as was the case with Examples 13 and 14 was, the mean fiber diameter found was in each case considerably closer to that expected dimensions. These examples thus demonstrate that high Flow rate of the purge gas is important to the according to the teaching of to realize the present coating geometry required.

Table VII

Claims (65)

1. A method of making a membrane comprising the following steps:

• a) dissolving a gas permeable polymer in a solvent so that a coating solution is obtained;
• b) selecting a microporous substrate with a pore size, on the basis of which one can effectively filter out the dissolved polymer from the coating solution, which substrate has a first and a second side;
• c) contacting the first side of the microporous substrate with the coating solution;
• d) causing the solvent to flow through the microporous substrate to the second side;
• e) removing the coating solution and the solvent from the membrane; and
• f) removing the solvent from the membrane, thereby forming a continuous, non-porous layer of the gas-permeable polymer on the first side,

wherein the gas permeable polymer is an amorphous copolymer of the compound perfluoro-2,2-dimethyl-1,3-dioxole, the oxygen permeability of which corresponds to a numerical value of at least 100 barrers at a temperature which is lower than the glass transition temperature of the amorphous copolymer. 2. The method according to claim 1, wherein steps (c) to (f) as long can be repeated until the non-porous layer of the gas-permeable polymer on the microporous substrate has a predetermined thickness.   3. The method of claim 1, wherein the non-porous layer is about 0.01 to is about 25 µm thick. 4. The method of claim 1, wherein it is the amorphous Copolymer is a copolymer based on the compound perfluoro-2,2-dimethyl-1,3-dioxole and a complementary amount of at least one further monomer which consists of has been selected from a group consisting of the following compounds: Tetrafluoroethylene, perfluoromethyl vinyl ether, vinylidene fluoride, hexafluoropropylene and Chlorotrifluoroethylene. 5. The method of claim 4, wherein it is the amorphous Copolymer around a dipolymer of the compounds perfluoro-2,2-dimethyl-1,3-dioxole and Tetrafluoroethylene. 6. The method of claim 5, wherein the dipolymer is 50 to 95 mole percent polymerized perfluoro-2,2-dimethyl-1,3-dioxole. 7. The method of claim 6, wherein the membrane is a Has oxygen / nitrogen selectivity of at least about 1.5: 1. 8. The method of claim 1, wherein it is the microporous Substrate is a polymer that has been selected from the group consisting of consists of the following materials: polyolefins; fluorinated polyolefins; Polysulfones; Cellulose ester polymers; Copolymers based on olefins; Copolymers based fluorinated olefins; Copolymers based on polysulfones; Copolymers on the Base of cellulose esters, and a mixture of the aforementioned materials. 9. The method of claim 8, wherein it is the microporous The substrate is polypropylene. 10. The method of claim 8, wherein it is the microporous Substrate is polyvinylidene fluoride.   11. The method of claim 8, wherein the substrate has a selection limit for polymers with a molecular weight which is lower than that Weight average molecular weight of the gas permeable polymer. 12. The method of claim 11, wherein the selection limit for the Molecular weight is at most 50,000. 13. The method of claim 11, wherein the pore size of the substrate is one Flow of gaseous oxygen through the uncoated substrate with a Flow rate that is at least five times as large as that Flow rate of gaseous oxygen through the non-porous layer. 14. The method of claim 13, wherein the pore size of the substrate is one Flow of gaseous oxygen corresponding to a numerical value of at least 10,000 gas permeability units enabled. 15. The method of claim 1, wherein it is the microporous Substrate is a hollow fiber. 16. The method of claim 1, wherein at most an amount of about 1 wt .-% gas permeable polymer is dissolved in the coating solution. 17. The method of claim 1, wherein the step in which the solvent is pulled off, contacting the non-porous layer with an injected gas comprises, wherein the blowing takes place at a speed which is sufficient to the dry non-porous layer with a uniform thickness on the membrane. 18. A method of manufacturing a gas filter comprising the following steps:

• a) dissolving a gas permeable polymer in a solvent so that a coating solution is obtained;
• b) Providing a filter module, which comprises the following components:
  • 1. an elongated housing with two ends, the housing defining a sleeve-side cavity;
  • 2. a first tube disk arranged at one end of the housing and having a first outer surface arranged outside the housing;
  • 3. a second tube disk arranged at the other end of the housing with a second outer surface arranged outside the housing;
  • 4. a plurality of microporous hollow fibers with open ends, which hollow fibers extend within the housing in the context of a substantially parallel arrangement from the first outer surface arranged outside the housing to the second outer surface arranged outside the housing, these hollow fibers together being one define tube-side cavity; and wherein one can effectively filter out the dissolved polymer from the coating solution based on the pore size of the hollow fibers; and
  • 5. at least one connection leading through the housing in the region of the sleeve-side cavity;
• c) causing the coating solution to flow through one of the sleeve-side cavities and the tube-side cavities;
• d) causing the solvent from the coating solution to flow through the microporous hollow fibers to the other side of the sleeve-side cavity and the tube-side cavity;
• e) removing the coating solution and the solvent from the module; and
• f) withdrawing the solvent from the hollow fibers, whereby a continuous, non-porous layer of the gas-permeable polymer is formed on one side of the hollow fibers.

19. The method of claim 18, further comprising an additional Step, in which the filter module is positioned so that the microporous hollow fibers are oriented vertically, before you start the flow of the Coating solution, and wherein one also causes the Coating solution flows upwards through the tube-side cavity. 20. The method of claim 19, wherein the step in which the  Solvent is withdrawn, the blowing of an inert gas through the tube side Cavity includes, at a rate sufficient to remove the solvent effectively peel off without a larger proportion of the hollow fibers through the polymer is clogged. 21. The method of claim 18, wherein steps (c) to (f) are as long can be repeated until the non-porous layer of the gas-permeable polymer on the Hollow fibers have a predetermined thickness. 22. The method of claim 18, wherein the gas permeable polymer is a amorphous copolymer of the compound perfluoro-2,2-dimethyl-1,3-dioxole, whose Oxygen permeability at a temperature lower than the glass transition temperature of the amorphous copolymer corresponds to a numerical value of at least 100 barrers. 23. The method of claim 22, wherein it is the amorphous Copolymer is a copolymer based on the compound perfluoro-2,2-dimethyl-1,3-dioxole and a complementary amount of at least one further monomer which consists of has been selected from a group consisting of the following compounds: Tetrafluoroethylene, perfluoromethyl vinyl ether, vinylidene fluoride, hexafluoropropylene and Chlorotrifluoroethylene. 24. The method of claim 23, wherein it is the amorphous Copolymer around a dipolymer of the compounds perfluoro-2,2-dimethyl-1,3-dioxole and Tetrafluoroethylene. 25. The method of claim 24, wherein the dipolymer is 50 to 95 mole percent polymerized perfluoro-2,2-dimethyl-1,3-dioxole. 26. The method of claim 18, wherein the gas filter is a Has oxygen / nitrogen selectivity of at least 1.5: 1. 27. The method of claim 18, wherein the hollow fibers are made of a polymer selected from the group consisting of the following materials: Polyolefins; fluorinated polyolefins; Polysulfones; Cellulose ester polymers; Copolymers  the base of olefins; Copolymers based on fluorinated olefins; Copolymers the base of polysulfones; Copolymers based on cellulose esters, and a Mixture of the aforementioned materials. 28. The method of claim 27, wherein the hollow fibers are made of polypropylene consist. 29. The method of claim 27, wherein the hollow fibers are made of Polyvinylidene fluoride exist. 30. The method of claim 27, wherein the hollow fibers are one Have selection limit for polymers with a molecular weight that is lower than the weight average molecular weight that the gas permeable polymer having. 31. The method of claim 30, wherein the selection limit for the Molecular weight is at most 50,000. 32. The method of claim 30, wherein the pore size of the hollow fibers allows gaseous oxygen to flow at a flow rate that is at least five times the flow rate of gaseous oxygen through the non-porous layer. 33. The method of claim 32, wherein the pore size of the hollow fibers a flow of gaseous oxygen corresponding to a numerical value of enables at least 10,000 gas permeability units. 34. The method of claim 18, wherein the pore size of the hollow fibers is approximately Is 0.005 to 0.1 µm. 35. The method of claim 18, wherein the non-porous layer is about 0.01 up to about 25 µm thick. 36. A gas filter comprising a membrane having an area corresponding to a filter surface suitable for a gas to flow therethrough so that suspended droplets can be separated from this gas, the membrane comprising the following components:
a microporous substrate with a pore size of about 0.005 to 0.1 µm; and
a non-porous, gas-permeable layer which is applied continuously to the substrate and to the entire area of the filter surface, which layer consists of an amorphous copolymer based on the compound perfluoro-2,2-dimethyl-1,3-dioxole and which layer also has an oxygen permeability of at least 100 barrers at a temperature below the glass transition point of the amorphous copolymer. 37. The gas filter according to claim 36, wherein the non-porous layer is about 0.01 to is about 25 µm thick. 38. The gas filter according to claim 36, wherein it is the amorphous copolymer a copolymer based on the compound perfluoro-2,2-dimethyl-1,3-dioxole and one complementary amount of at least one further monomer, which consists of a Group has been selected consisting of the following compounds: tetrafluoroethylene, Perfluoromethyl vinyl ether, vinylidene fluoride, hexafluoropropylene and chlorotrifluoroethylene. 39. The gas filter according to claim 36, wherein it is the amorphous copolymer a dipolymer of the compounds perfluoro-2,2-dimethyl-1,3-dioxole and tetrafluoroethylene acts. 40. The gas filter according to claim 39, wherein the dipolymer 50 to 95 mol% polymerized perfluoro-2,2-dimethyl-1,3-dioxole. 41. The gas filter according to claim 40, wherein the gas permeable structure is a Has oxygen / nitrogen selectivity of at least 1.5: 1. 42. The gas filter according to claim 36, wherein the amorphous copolymer is one Glass transition temperature of at least 115 ° C.   43. The gas filter according to claim 36, wherein the non-porous layer is a Oxygen permeability corresponding to a numerical value of at least 200 barrers having. 44. The gas filter according to claim 43, wherein the non-porous layer is a Oxygen permeability corresponding to a numerical value of at least 500 barrers having. 45. The gas filter according to claim 36, wherein it is the microporous Substrate is a polymer that has been selected from the group consisting of consists of the following materials: polyolefins; fluorinated polyolefins; Polysulfones; Cellulose ester polymers; Copolymers based on polyolefins; Copolymers on the Based on fluorinated polyolefins; Copolymers based on polysulfones; Copolymers based on cellulose esters, and a mixture of the aforementioned materials. 46. The gas filter according to claim 45, wherein the microporous Substrate made of polyvinylidene fluoride. 47. The gas filter according to claim 45, wherein the microporous The substrate is made of polypropylene. 48. The gas filter according to claim 36, wherein it is the microporous Substrate is a hollow fiber. 49. A method for separating a gas from an aerosol, which comprises the following measure: flowing a gas through an area corresponding to the filter surface of a membrane, which membrane comprises the following components:
a microporous substrate; and
a non-porous, gas-permeable layer which is applied continuously on the substrate and on the entire area corresponding to the filter surface, which layer consists of an amorphous copolymer based on the compound perfluoro-2,2-dimethyl-1,3-dioxole and which layer also has an oxygen permeability corresponding to a numerical value of at least 100 barrers at a temperature below the glass transition point of the amorphous copolymer. 50. The method of claim 49, wherein the non-porous layer is about 0.01 up to about 25 µm thick. 51. The method of claim 50, wherein it is the amorphous Copolymer is a copolymer based on the compound perfluoro-2,2-dimethyl-1,3-dioxole and a complementary amount of at least one further monomer which consists of has been selected from a group consisting of the following compounds: Tetrafluoroethylene, perfluoromethyl vinyl ether, vinylidene fluoride, hexafluoropropylene and Chlorotrifluoroethylene. 52. The method of claim 51, wherein it is the amorphous Copolymer around a dipolymer of the compounds perfluoro-2,2-dimethyl-1,3-dioxole and Tetrafluoroethylene. 53. The method of claim 52, wherein the dipolymer is 50 to 95 mole percent polymerized perfluoro-2,2-dimethyl-1,3-dioxole. 54. The method of claim 53, wherein the gas permeable structure is a Has oxygen / nitrogen selectivity of at least 1.5: 1. 55. The method of claim 49, wherein the amorphous copolymer is a Glass transition temperature of at least 115 ° C. 56. The method of claim 49, wherein the non-porous layer is a Oxygen permeability corresponding to a numerical value of at least 200 barrers having.   57. The method of claim 56, wherein the non-porous layer is a Oxygen permeability corresponding to a numerical value of at least 500 barrers having. 58. The method of claim 49, wherein it is the microporous Substrate is a polymer that has been selected from the group consisting of consists of the following materials: polyolefins; fluorinated polyolefins; Polysulfones; Cellulose ester polymers; Copolymers based on polyolefins; Copolymers on the Based on fluorinated polyolefins; Copolymers based on polysulfones; Copolymers based on cellulose esters, and a mixture of the aforementioned materials. 59. The method of claim 58, wherein the microporous Substrate made of polyvinylidene fluoride. 60. The method of claim 58, wherein the microporous The substrate is made of polypropylene. 61. The method of claim 49, wherein it is the microporous Substrate is a hollow fiber. 62. A method of using a gas filter to remove particles from a clean room in a factory for the production of microelectronic Components, the gas filter comprising a membrane, which includes the following components: a microporous substrate with a pore size of about 0.005 to 0.1 µm; and a non-porous, gas-permeable layer that is on the substrate and on the whole The area corresponding to the filter surface is applied continuously Layer of an amorphous copolymer based on the compound perfluoro-2,2- Dimethyl-1,3-dioxole and which layer is also a Oxygen permeability corresponding to a numerical value of at least 100 barrers  at a temperature below the glass transition point of the amorphous copolymer having. 63. A method of using a gas filter to remove harmful substances from the air in a medical facility, the gas filter comprising a membrane including the following components:
a microporous substrate with a pore size of about 0.005 to 0.1 µm; and
a non-porous, gas-permeable layer which is applied continuously on the substrate and on the entire area corresponding to the filter surface, which layer consists of an amorphous copolymer based on the compound perfluoro-2,2-dimethyl-1,3-dioxole and which layer also has an oxygen permeability corresponding to a numerical value of at least 100 barrers at a temperature below the glass transition point of the amorphous copolymer. 64. The method of claim 1, wherein the membrane is made of a hollow fiber is different. 65. A method of making a membrane comprising the following steps:

• a) dissolving a gas permeable polymer in a solvent so that a coating solution is obtained;
• b) selecting a microporous substrate with a pore size, on the basis of which one can effectively filter out the dissolved polymer from the coating solution, which substrate has a first and a second side;
• c) contacting the first side of the microporous substrate with the coating solution;
• d) causing the solvent to flow through the microporous substrate to the second side;
• e) removing the coating solution and the solvent from the membrane; and
• f) removing the solvent from the membrane, thereby forming a continuous, non-porous layer of the gas-permeable polymer on the first side,

the microporous structure comprising a hollow fiber defining an inner and an outer surface such that the first side corresponds to the inner surface and the second side corresponds to the outer surface.